1. Field of the Invention
The present invention relates to a data recording method, and particularly to a method for recording intermittently data trains each having a fixed word length on a recording medium.
2. Description of the Prior Art
FIG. 1 is a diagram showing a data recording format employed in a data recording apparatus, such as an optical disk apparatus, according to a conventional data recording method. The recording format as shown in FIG. 1 is disclosed in, for example, "Mass Storage Optical Disk File Apparatus Capable of Recording Code Information" by Yoshito Sumida et al., NIKKEI ELECTRONICS (Japanese Periodical), Nov. 21, 1983, pp. 189-213.
Referring to FIG. 1, a recording format employed in an optical disk apparatus comprises a header portion 1 which is recorded on an optical disk (not shown) in advance to indicate the position clearly in which one of the data trains should be recorded for intermittent recording of the data trains, a preamble portion 2 for performing bit synchronization, a synchronizing pattern portion 3 for indicating the head position of one of the data trains to be recorded clearly, a data portion 4 in which one of the data trains should be recorded and a gap portion 5 for separating this recorded data train from the next data train to be recorded.
FIG. 2 is a diagram illustrating the data portion 4 in the recording format shown in FIG. 1 in detail. The detailed description as to FIG. 2 is also provided in the above specified Japanese periodical, pp. 205. Referring to FIG. 2, the data portion 4 generally comprises a user data portion 41, a check data portion 42 for error check and correction, and a resynchronizing pattern portion 43 for recovering data synchronization. More particularly, the user data portion 41 is capable of storing the data of 528 bytes (D.sub.1 to D.sub.528), which data portion is divided into 16 pieces. Each of these pieces includes 33 bytes of user data. In addition, the check data portion 42 includes check data of 64 bytes (C.sub.1 to C.sub.64), and such check data portion is also divided into 16 pieces, each piece including 4 bytes of check data. These pieces of check data are added to the above described pieces of user data correspondingly, so that user data D.sub.1 to D.sub.33 is combined with check data C.sub.1 to C.sub.4 to form a first code word, user data D.sub.34 to D.sub.66 is combined with check data C.sub.5 to C.sub.8 to form a second code word, . . . , and user data D.sub.496 to D.sub.528 is combined with check data C.sub.61 to C.sub.64 to form a 16th code word. The resynchronizing pattern portion 43 includes the data of 36 bytes (R.sub.1 to R.sub.36).
In the recording format as shown in FIG. 2, one of the data trains is recorded in the data portion 4 in such a manner that the first byte in the first code word (D.sub.1), the first byte in the second code word (D.sub.34), . . . , the first byte in the 16th code word (D.sub.496), and the resynchronizing pattern portion (R.sub.1) are recorded in sequence in the first recording cycle, and then the second byte in the first code word (D.sub.2), the second byte in the second code word (D.sub.35), . . . , the second byte in the 16th code word (D.sub.497), and the resynchronizing pattern portion (R.sub.2) are recorded in sequence in the second recording cycle, and then such a recording cycle of 17 bytes from the first code word to the resynchronizing pattern portion is repeated continuously until recording of the last check data C.sub.64 is completed. Namely, even if data synchronization of the regenerated signal is missed, such data synchronization could be recovered within every resynchronizing pattern since the resynchronizing pattern data bytes R.sub.1 to R.sub.36 are added to the data train for every 16 bytes of data to be recorded in accordance with the above described recording sequence. Accordingly, burst-like errors hardly occur in every code word.
Table 1 describes correcting capability of various recording formats, each with "Reed Solomon Coding" being applied to. In this Table 1, "n" means the total number of bytes in a single code word, "k" means the number of bytes of user data in a single code word, "n-k" means the number of bytes of check data in a single code word, "T" means the number of correctable bytes in a single code word, "m" means the number of code words in the data train and "Ps" means error bytes probability. In this case, the total number of bytes of user data in the single data train equals to k.times.m=528 and the total number of bytes of check data in the single data train equals (n-k).times.m=64, and these numbers are assumed to be constant. This Table 1 shows three kinds of recording formats A, B and C, depending on the length of "n".
TABLE 1 __________________________________________________________________________ A B C __________________________________________________________________________ NUMBER OF BYTES OF USER 3 66 132 DATA IN A SINGLE CODE WORD (k) NUMBER OF BYTES OF CHECK DATA 4 8 6 IN A SINGLE CODE WORD (n-k) NUMBER OF CORRECTABLE BYTES 2 4 8 (T) NUMBER OF CODE WORDS 6 8 4 (m) CODING EFFICIENCY 0.89 0.89 0.89 (USER DATA/TOTAL DATA) PROBABILITY OF UNCORRECTABLE 1.2 .times. 10.sup.5 Ps.sup.3 1.3 .times. 10.sup.8 Ps.sup.5 2.9 .times. 10.sup.14 Ps.sup.9 BYTES (Ps: ERROR BYTES PROBABILITY) PROBABILITY OF UNCORRECTABLE 1.2 .times. 10.sup.-7 1.3 .times. 10.sup.-12 2.9 .times. 10.sup.-22 BYTES (Ps = 10.sup.-4) __________________________________________________________________________
As seen from Table 1, among various recording formats each having a common coding efficiency of 0.89, probability of uncorrectable byte of the recording format in which the total number of bytes in a single code word "n" is large, such as the format C, is lower than that of the other formats, such as the formats A and B, and such recording format C whose "n" is large has high correcting capability.
However, if the total number of bytes of user data in the single data train is constant as described in the foregoing, the number of code words "m" becomes smaller when the total number of bytes in a single code word "n" becomes large, causing a problem that the ratio of the resynchronizing pattern portion in the data portion increases.
Although such error correcting function is disclosed in Japanese Patent Laying-Open Gazette Nos. 65320/1981 and 185035/1984, the above described problem could not be solved by the disclosures in these references.